In the art of forming carbonaceous bodies, especially synthetic-graphite bodies and graphite or graphite-like bodies, it is frequently desirable to use powdered carbonaceous materials, some of which may be waste products or by-products of other processes. The powdered materials may include electrographite and natural graphite, but generally are milled or ground petroleum coke, carbon black and other carbonaceous materials which may be powdered or pulverized before use or may be obtained naturally in a powdered or pulverulent state.
Graphite and synthetic-graphite bodies have been employed heretofore for many purposes and in various industries. They have particular value, however, in nuclear-reactor technology and preferably in high-temperature gas-cooled nuclear reactors in which the graphitic bodies may be used as part of the nuclear reactor core structure, as enclosures or casings for nuclear-fuel elements or for breeder elements participating in a breeding nuclear reaction, and as outer coverings of nuclear reactor fuel or breeder particles.
In the commonly assigned concurrently filed copending Application Ser. No. 267,479 entitled "METHOD OF MAKING SHAPED CARBONACEOUS BODIES" and filed by three of the present applicants, there is described a method of making shaped synthetic-graphite of graphitic bodies using synthetic-resin binders, tar, or pitch. The binder, preferably a phenol-formaldehyde resin, is carbonizable and, after the moist body is formed from coated carbonaceous filler particles, the structure is dried and then cokefied in accordance with conventional techniques.
Graphite or graphite-like materials are especially desirable in the production of fuel elements or other structural parts of gas-cooled high-temperature nuclear reactors because of the refractory character of the material and its neutron cross section. After the mixture is shaped into the desired configuration, it is heated to about 800.degree. C. or higher to carbonize the binder, the cokefication process being as well as graphitization process in accordance with conventional teachings. In this regard reference may be made to the publication "Carbon and Graphite Handbook", Charles L. Mantell, Interscience Publishers, New York 1968, p. 266.
In conventional systems for providing a shapable carbon-containing mass for subsequent graphitization and cokefication, it has been the common practice to simply blend the carbon particles, usually electrographite, natural graphite, comminuted petroleum coke and carbon black, with the synthetic-resin binder or a cokefiable binder of a bituminous base, e.g. tar or pitch. The blended mass is then shaped and heated.
These conventional processes, however, have been found to be disadvantageous in that the distribution of the binder is found to be nonuniform in the shaped body because the binder does not necessarily uniformly cost all of the grains of the filler. During the process of evaporation of volatile components of the binder system, the binder tends to concentrate in certain areas free from the binder material. As a result, the cokefied or graphitized mass is found to be less homogeneous than is desirable and lacks uniform porosity and other advantageous mechanical properties.